1. Field of the Invention
This invention relates to the field of removable and replaceable light bulb units for slit lamps.
2. Background Art
Slit lamps are widely used by ophthalmologists and optometrists to examine the human eye. In use, such lamps provide an illumination beam through a narrow slit which is then directed into the eye. The illumination beam is normally directed toward the eye along a horizontal axis and the slit lamp includes a microscope for examination by the operator of the area of the eye illuminated by the beam. To provide the beam and permit examination, the light source is commonly mounted to direct the light beam downwardly onto a mirror where it is then reflected horizontally into the eye. In operation, the light source or bulb is actually positioned upstream of one or more focusing lenses and must be precisely positioned within the slit lamp relative to these lenses both vertically and horizontally. Additionally, the filament of the light source or bulb must also be angularly oriented correctly about a vertical axis.
Various techniques have been used to properly position the light source or bulb within the slit lamp. Some techniques are more popular than others but they all strive to provide a simple and effective way to insert and replace the bulb without disturbing the alignment of the other operating members of the slit lamp. This is particularly important since burned out bulbs are usually removed and replaced by the ophthalmologist or optometrist himself or someone in his office.
In this regard, one of the most popular and widely used alignment techniques is to use a circular, disc-shaped base member to which an incandescent bulb is mounted. The circular base member abuts permanent structure in the slit lamp and not only serves to properly center the filament of the bulb horizontally (i.e., left and right relative to focusing lenses) but also vertically relative to the focusing lenses. Additionally, the circular perimeter of the base member is notched and cooperates with a locating pin on the slit lamp to correctly orient the filament of the bulb about a vertical axis. However, to date, this popular and effective technique using a circular base member has only been adapted to incandescent light bulbs wherein the base of the incandescent bulb fits directly into the circular base member. Incandescent bulbs have been used in slit lamps for years but their light tends to have a yellow tint at least in comparison with the almost pure white light of the more modern halogen bulbs. This yellow tint is highly undesirable in the examination of the human eye where true color is essential; yet, no design to date has been able to adapt a halogen bulb to a circular, disc-shaped base member so that it can be used as an original or replacement bulb in slit lamp models such as the Haag-Streit Model 900.
With this background, the present invention was developed. With the present invention, halogen bulbs can now be adapted for use with slit lamps built to receive circular, disc-shaped base members such as the Haag-Streit Model 900. Further, with the present invention, a reflector can additionally be used wherein nearly all of of the light emanating from the filament of the halogen bulb can be directed toward the eye under examination.